473 
Influence of Carbon Dioxide. IV. 
Seed-coat rings (a) were obtained from thick median sections of seeds. 
These seed-coat rings varied in breadth from 2 p, to 20 /x, a micrometer reading 
being taken in each case at the point of Tupture. In each experiment 
a number of rings from different seeds were taken and the average weight 
supported (in grammes per i /x of breadth) was calculated. This is possible 
since the relationship between the breadth of the ring and its breaking 
strain was found to be approximately linear over the range used. The 
sensitiveness of the apparatus was increased by making the arms of the 
balance of unequal length. 
Table XV. 
Mechanical Resistance of the Testa-breaking Strain of Seed-coat Rings. 
N on-inhibited Seeds. 
Number of 
Time in gerniinator. seed-coats 
tested. 
3l hrs. r i 
6 hrs. 9 
io hrs. (testas only soaked) 8 
io hrs. (whole seeds soaked) 9 
2 days (3 actually germinating) 7 
3 days (kept under water) 7 
Average weight supported 
by testa-ring per p 
of breadth. 
3*3 grm. 
2*3 grm. 
i *9 g rm * 
I# 4 grm. 
i*o grm. 
1*2 grm. 
1 st Sample. 
Time after revioval from the 
inhibitory gas-niixture . 
5 days * 
15 days 
23 days 
2nd Sample. 
Immediately 
5 da ys 
inhibited Seeds. 
Number of seed- 
cbdts tested. 
Average id eight supported by testa- 
ring per /t of breadth. 
13 
2»9 grm. 
i-3 grm. 
o‘9 grm. 
10 
10 
1*2 grm. 
o ; 9 grm. 
* 
No germinations occurred in this sample of inhibited seeds up to a period of two months. 
The results of these direct measurements indicate that the condition of 
secondary dormancy in White Mustard seeds cannot be attributed to an 
increase in the breaking strait! of the seed-coats by which the growth of the 
radicle is prevented. When the lowest values obtained for seeds undoubtedly 
in a condition of secondary dormancy are compared with the values obtained 
for untreated seeds oil the point of germination, the figures are from 1*3 to 
0*9 as against from 1*4 to i-o. The results further indicate that the breaking 
strain of the seed-coat is subject to considerable variation. In the case of 
freshly soaked untreated seed it is clear that the breaking strain of the seed- 
coat continues to fall for some time after they have become water-saturated 
and pliant. In the case of inhibited seeds showing secondary dormancy, 
continued exposure on damp sand results in a gradual decrease in the 
